1. Field of this Invention
This invention is related to pressure control means for closed-loop, incompressible-liquid circulating, hydronic heating systems.
2. Description of the Prior Art
In all closed liquid circulating systems, some means must be provided to accommodate the expansion and contraction of the liquid within the circulating system, which usually results from thermal expansion of the contained liquid. Typically, this means has a pressurized accumulator tank connected to the circulating system such that when the liquid expands, a portion of it passes into the accumulator tank to prevent undue pressure buildup within the circulating system. The accumulator tank also provides a small supply of liquid to the circulating system when the liquid in the circulating system cools to prevent air from entering the circulating system and to provide a more consistent heat transfer. In the past, such circulating systems have required the accumulator tank to be pressurized, since the liquid within the circulating system itself is also pressurized. The requirement of a pressurized vessel has increased the cost and complexity of such liquid circulating systems and has increased the maintenance requirements due to the need for inspecting the pressurized vessel and its associated components.
The use of a Venturi structure in a water circulating system is known in the art, and is specifically shown in U.S. Pat. No. 2,265,108. The patent, however, utilizes the Venturi structure interconnected between a storage tank, a heater and an incoming water supply such that the action of the incoming water sypply passing through the Venturi creates a low pressure area at the Venturi throat which serves to stimulate the circulation of the water from the storage tank. Thus, the patent utilizes the Venturi structure as a jet-pump device to assist the circulation of the water within the fluid system.
The use of an ejector or jet-pump structure to circulate water through a system, or assist in such circulation, is well-known and is shown by the following U.S. Pat. Nos. 566,904, 1,418,583, 2,404,114, 2,843,142, 3,274,065 and 3,730,646. However, in none of these patents is there a disclosure that a Venturi structure can be interposed between an open storage tank and a closed liquid circulating system such that the liquid circulating means passes a portion of the liquid through the Venturi to control the addition or venting of liquid between the pressurized system and the atmospheric storage tank to control pressure.
It is also known to utilize a water storage tank open to atmospheric pressure in a liquid circulating system, as shown in U.S. Pat No. 3,554,441. The storage vessel is connected to the liquid circulating system so as to allow water to flow into and out of the system depending upon the relative difference between the system pressure and the pressure in the vessel. Overflow of this vessel is prevented by interconnecting it with a secondary storage vessel located at a lower level.
U.S. Pat. No. 667,559 discloses a closed loop fluid circulating system having a pump. The patent has apparatus that contains a Venturi tube, but the flow pattern is into the diffuser and then out of the nozzle. The diffuser relatively slowly causes a decrease in pressure and then the fluid literally explodes out of the narrow end of the nozzle into the rapidly expanding nozzle. This action is not that of a Venturi tube, but is certainly the effective mixing scheme which the patent seeks. The patent deals with a method of adding liquid from a reservoir to a steam boiler. In a steam boiler pressure is governed by the temperature of the steam, which in turn is affected by the amount of heat addition. Steam pressure cannot be controlled by changing the liquid inventory. Also, the patent does not control the pressure in the circulating system by means of the Venturi tube.
U.S. Pat. No. 3,614,266 deals with an oil pump for a car power steering system. The patent does not disclose a Venturi tube and only teaches a nozzle without any diffuser.
German OS No. 2,948,029 and U.S. Pat. No. 3,987,628 (Gassman) deal with a charge pump augmenting device for hydraulic systems of motor vehicles. The concept of Gassman is to augment fluid flow by supplying fluid from a fluid reservoir to maintain a predetermined pressure at the main pumps. But Gassman does not control the pressure by allowing flow both from and to the separate reservoir via the Venturi. Gassman prevents the flow of fluid from the Venturi chamber to the reservoir. There is return fluid flow to the fluid reservoir in Gassman, but it is via a line which is not associated in any way with the Venturi. Gassman's system is not a closed-loop circulating system as all of the return flow is to the reservoir. Gassman uses control and check valves to obtain pressure control.